SINGLET ENERGY-TRANSFER IN BIS(PHENYLETHYNYL)PHENYLENE-BRIDGED ZINC-FREE BASE HYBRID DIPORPHYRINS

A set of bis(phenylethynyl)phenylene-bridged diporphyrins 1-3 has been prepared by the acid-catalysed double condensation reaction of bis(4- formylphenylethynyl)benzene 8 and 9, and 3,5-di-tert-butylbenzaldehyde 11 with bis(3-hexyl-4-methylpyrrol-2-yl)methane 12 or the Pd-0-cataly sed coupling reaction of acetylene-substituted porphyrin 14 with 1,4-d iiodobenzene. Intramolecular singlet excitation energy transfer in Zn- free base hybrid diporphyrins 1-3(ZH) has been studied by picosecond t ime-resolved fluorescence spectroscopy. The determined k(EN), values a re in the order of 1(ZH) > 2(ZH) approximate to 3(ZH). The energy tran sfer mechanism is discussed in terms of varying contribution of throug h-space and through-bond interactions.